For PA subscriptions, upgrade of one resource provides a possibility to set other resources as unlimited despite hosting plan settings.
Also, Number of IIS application pools limit is not related to IIS Webspace resource.
Software issue #PPA-3047. Improper configuration of Service Template resources (IIS Application Pools) leads to failed synchronization between Plesk and PA part.
Set correct resource limits in Service template or in particular Subscription resources: Number of IIS application pools, MySQL, MSSQL databases etc. (limit should be greater or equal to actual resource usage)
Synchronize resource usage for affected subscription using the
# /usr/local/ppa/bin/sync_resource_usage --sub_id=54
54 is the ID the of affected PA subscription.